将加速的数组表示转换为repa的U数组表示

Question

我想将加速数组转换为repa数组，然后使用repa的writeImageToBMP将数组写入BMP文件。忽略存在这样一个函数的事实-io，我只是用它作为一个问题的例子。采取：

{-# LANGUAGE ScopedTypeVariables #-}
import qualified Data.Array.Accelerate.Interpreter as A (run)
import Data.Array.Accelerate
import qualified Data.Array.Accelerate as A
import qualified Data.Array.Accelerate.IO as A
import qualified Data.Array.Repa as Repa
import qualified Data.Array.Repa.IO.BMP as Repa
import GHC.Word

main :: IO ()
main = do
  let accelArr = A.fromList
                 (Z :. (2::Int) :. (1::Int))
                 ([(1,2,3),(4,5,6)] :: [(Word8,Word8,Word8)])
      computation :: A.Acc (A.Array A.DIM2 (Word8,Word8,Word8))
      computation = A.map
       (\triple ->
           let (r',g',b') = unlift triple :: (Exp Word8,Exp Word8,Exp Word8)
           in lift (constant 0,g',b')) (use accelArr)
      repaArr :: Repa.Array A.A Repa.DIM2 (Word8,Word8,Word8)
      repaArr = A.toRepa (A.run computation)
  Repa.writeImageToBMP "out_repa.bmp" repaArr

这些包可以加速、加速-io、repa和repa来编译这个代码.

这不能编译，因为repa中的writeImageToBmp类型是：

writeImageToBMP
  :: FilePath
  -> Repa.Array Repa.U Repa.DIM2 (Word8, Word8, Word8)
  -> IO ()

其中U表示repa中的清单数组。GHC错误是：

Couldn't match type ‘A.A’ with ‘Repa.U’
Expected type: Repa.Array Repa.U Repa.DIM2 (Word8, Word8, Word8)
  Actual type: Repa.Array A.A Repa.DIM2 (Word8, Word8, Word8)
In the second argument of ‘Repa.writeImageToBMP’, namely ‘repaArr’
In a stmt of a 'do' block:
  Repa.writeImageToBMP "out_repa.bmp" repaArr

repaArr的类型是：

Repa.Array A.A Repa.DIM2 (Word8,Word8,Word8)

这就是为什么GHC抱怨这是writeImageToBMP的一个论点。

问题：如何将加速数组表示A转换为repa清单数组表示U，以便在其上调用writeImageToBMP？

Answer 1

注意，computeS、computeP、copyS和copyP在Data.Array.Repa中具有这样的签名：

...constraints... => Array r1 sh e -> m (Array r2 sh e)

因此，它们是允许您在不同Repa表示(即转换r1 -> r2)之间进行转换的函数。

考虑到这一点，我需要输入以下代码：

main :: IO ()
main = do
  let accelArr = A.fromList
                 (Z :. (2::Int) :. (1::Int))
                 ([(1,2,3),(4,5,6)] :: [(Word8,Word8,Word8)])
      computation :: A.Acc (A.Array A.DIM2 (Word8,Word8,Word8))
      computation = A.map
       (\triple ->
           let (r',g',b') = unlift triple :: (Exp Word8,Exp Word8,Exp Word8)
           in lift (constant 0,g',b')) (use accelArr)
      repaArr :: Repa.Array A.A Repa.DIM2 (Word8,Word8,Word8)
      repaArr = A.toRepa (A.run computation)
  zzz <- Repa.copyP repaArr
  Repa.writeImageToBMP "out_repa.bmp" zzz

您也可以在这里使用Repa.copyS。